Optical communication networks are built from various components acting as, e.g., sources, guides, processing units, and sinks of optical signals. Such components, e.g., lasers, fibers, amplifiers, splitters and combiners, switches, and photoelectric receivers, may be built using different technologies. Common properties, however, of such components are a degradation of performance parameters over time caused by aging and their susceptibility to mechanical and/or other physical impacts, which may result in further deterioration regarding their performance. Other effects and sources of impairments of the system performance may depend on the number and density of optical channels sharing common physical resources like, e.g., fibers, and from the load of the network or individual network components. Most of these effects may not have a significant impact during an early phase of a network's lifetime, but aggravate over time with increasing network utilization and age of its components. Such deteriorating effects may further accumulate along an end-to-end communication path.
Network planning and dimensioning thus has to take into account such deteriorating effects in order to ensure the performance for end-to-end paths during and until the end of the network's planned lifetime.
In order to cope with the effects as mentioned above, optical communication network planning and dimensioning usually starts from a so-called end-of-life performance, i.e. a target level of performance intended to be met by a completely equipped and fully loaded network under worst-case conditions assumed at the end of its scheduled lifetime. Such worst-case conditions include an expected amount of degradation due to aging of the components and an additional margin to cover effects of mechanical and other physical or chemical impacts that might be experienced during the lifetime of the system.
Network planning and dimensioning starts with an end-of-life target performance, adds a margin for mechanical and physical or chemical impacts, and the expected deterioration due to aging. FIG. 1 illustrates in an example the principles of system planning together with an example of a potential real-life behavior of a system. In order to meet the end-of-life requirements, the network has to be planned and dimensioned according to an initial system performance determined from the end-of-life target performance and the respective margins for aging and other impacts.
As shown in FIG. 1, real system performance degrades over time due to aging. The shape of the aging curve can be of various forms, e.g., concave, convex, regular or irregular; usually the curve decreases more or less continuously. Discontinuities or steps may occur due to mechanical or other physical impacts on the equipment.
In case of proper dimensioning of the system, i.e. if a well dimensioned margin is added during initial network planning, such margin will suffice for performance degradation over the lifetime of the system and the remaining system performance at the end-of-life will at least meet the planned target. Consequently, the system will be capable of supporting the variable and usually increasing service demand and the resulting system usage during the full lifetime period.
Insufficient dimensioning on the other hand results in the system performance not reaching the end-of-life target level. This may result in service degradations or incapabilities to provide services or service levels as initially planned. FIG. 2 illustrates an example of potential effects of insufficient dimensioning of a system. The example shows a real system performance at a time T1 undergoing the planned target level and the system being unable to fulfill the current service demand at a time T2. As a consequence, the system will exhibit service degradation up to a complete outage of some or all of its service channels.
EP 1 636 929 B1 discloses a method for the pre-emphasis of optical wavelength division multiplex signals wherein in order to achieve preset optical signal-to-noise ratios (OSNR), the power settings of individual channel signals or groups of channel signals are adjusted at their entry points (i.e. related network elements) to the network. Channel or group of channel specific OSNRs are evaluated and adjusted relative to each other based on pre-assigned profiles provided by a network planning tool. The pre-assigned profiles are static and either calculated from theoretically expected path characteristics or determined by related noise measurements.
However, EP 1 636 929 B1 relates to static conditions only and does not refer to aging or other lifetime impacts on network parameters. The solution disclosed in EP 1 636 929 B1 may be used to determine discrete power level values to be assigned to channels and groups of channels at the start of the lifetime or at a certain point in the lifetime of a system.
[http://www.netfast.com/xq/asp/qx/PDF/Alcatel/1830_PSS_bro.pdf] is an advertising brochure promoting a photonic services switch and discloses a so-called “wavelength tracker technology” allegedly capable of “end-to-end power control, monitoring, tracing and fault localization for each individual wavelength channel”. The solution is focused on wavelength path management to enable “quick troubleshooting and fault isolation” in case of immediate service impairments or outages.
Accounting for end-of-life worst-case conditions at the start-of-life of an optical communication network requires huge performance margins and results in a network being significantly over-dimensioned. It requires a high upfront investment, i.e. capital expenditures (CAPEX), even if the network usage starts at a low level and (slowly) develops growth over time. In many scenarios when a system has been up and running for some time it then becomes apparent that far less resources spent in dimensioning the network would have been fully sufficient. On the other hand, even a huge margin may not suffice, if extreme mechanical or other physical stress leads to extraordinary deteriorations of the system performance.